| Proposal of new test signal for amplifiers, with regard to HF interference - Click HERE for Original Thread |
| darkfenriz |
Sine mixed with square?
Such signals were used to measure TIM in 70's.
If your square is steep enough, you can actually observe slew limitation at output of some circuits. I think that 30kHz square should be at least 100 times lower in amplitude then.
regards
Adam |
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| PMA |
Adam,
I know DIM30 and DIM100 signals. They consist of 3.18kHz square and 15kHz sine. Square amplitude is 4:1 to sine.
May goal is very different. To simulate HF content at player output. 30 kHz corresponds to switching frequency of DC-DC converter. Square simulates harmonic content of fast impulses with 30 kHz repetition. Small square amplitude corresponds to interference amplitude related to useful signal.
Cheers,
Pavel |
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| darkfenriz |
Still, I'd prefer triangle.
First it is more similar to SMPS voltage ripple, second there is no fear of slew overload a circuit with a triangle. One the other hand it has -12dB/oct spectrum vs. -6dB/oct for square.
Just my suggestion.
regards
Adam |
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| PMA |
Adam,
I do not think so. The HF impulse residuals at CD player output have rise time of 10ns. Just a derivative of square. Triangle is integral of square and thus very easy signal for amplifier.
I am not afraid of the slew rate limitation. Square amplitude in my test is 30dB under sine amplitude.
For me, amplifier must whithstand square wave test, 10kHz at 50% power for one hour into load. If not, the amplifier is not worth any consideration for me.
Cheers,
Pavel |
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| lumanauw |
Hi, PMA,
Good one :up:
Since the disturbance is unadvoidable in home audio environment these days, could this thread gives solution how to advoid those HF intermodulation with music signal?
BTW, this is about square wave and audio signal (sinusoidal signals)
http://www.diyaudio.com/forums/show...6689#post806689 |
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| PMA |
| quote: | Originally posted by lumanauw
Hi, PMA,
Good one :up:
Since the disturbance is unadvoidable in home audio environment these days, could this thread gives solution how to advoid those HF intermodulation with music signal? |
David,
this is what I have been permanently trying to work on. Recommendations would cover construction, wiring, input filters. Unfortunately, audio is only my hobby and my time for it is limited. On the other hand, I design instruments for operation in harsh EMI invironment as my professional job. I will try to give some recommendations, after I have time to translate them from my similar document in Czech language.
Regards,
Pavel |
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| PMA |
| Right now, my colleague Vladimir has made a similar test on commercial SONY amplifier. Test signals were 6kHz sine + 31kHz square, amplitude ratio same as in my measurements. 16W into 4ohm load. Please compare with my Symasym measurement in post no. 1 of this thread. |
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| PMA |
| This is Symasym for 1kHz sine + 34kHz square: |
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| MikeB |
| quote: | Originally posted by PMA
Right now, my colleague Vladimir has made a similar test on commercial SONY amplifier. Test signals were 6kHz sine + 31kHz square, amplitude ratio same as in my measurements. 16W into 4ohm load. Please compare with my Symasym measurement in post no. 1 of this thread. |
:cannotbe: Looks horrible !
Can you repeat your measuring also with 6khz sine ? Or Vladimir with 1khz ?
As reference the sony should also be measured with pure 6khz ?
Mike |
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| PMA |
Hi Michael,
the SONY is horrible, I am attaching pure 6kHz measurement.
Regarding measurements, Vladimir has only fix frequency generator 6kHz. This generator is extremely pure, like 0.0002%.
I can repeat Symasym measurement with 6kHz sine + 34kHz square, but not now. You do not have to worry, Symasym will be much much better than the SONY.
Cheers,
Pavel
P.S. Someone might disagree, but for me amplifiers with 0.1% THD and a lot of spectral lines are horrible. And they do sound horrible. |
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| MikeB |
| quote: | Originally posted by PMA
Hi Michael,
the SONY is horrible, I am attaching pure 6kHz measurement.
Regarding measurements, Vladimir has only fix frequency generator 6kHz. This generator is extremely pure, like 0.0002%.
I can repeat Symasym measurement with 6kHz sine + 34kHz square, but not now. You do not have to worry, Symasym will be much much better than the SONY.
Cheers,
Pavel
P.S. Someone might disagree, but for me amplifiers with 0.1% THD and a lot of spectral lines are horrible. And they do sound horrible. |
Pavel, they really sell THAT ? No wonder this forum is so busy...
About THD, 0.1% might be still okay, that's what i measured from speakers. But the amount of spectral lines shown by the sony is completely unacceptable. I wonder how they achieved that...
Attached is a measurement from a (unfinished) speaker, done with a mic connected to a bad soundcard. (Visaton AL130 + G20SC) The distortions might even be dominated by the mic-input. Hey, the tweeter seems to have lower distortion than the sony... (Sorry for beeing OT)
Mike |
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| PMA |
Michael,
That is what it is all about. As long as distortion is only 2nd and 3rd harmonic, we can digest it. The neverending chain of spectral lines, shown by Sony, even at some 0.1%, is totally unacceptable.
No distortion is good, and high order distortion is the worst.
But - regarding HF intermodulation - even 2nd and 3rd harmonic distortion of higher level will bring unacceplable intermodulation products. See post no. 1 here.
Cheers,
Pavel |
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| MikeB |
Pavel, yes, any distortion will create IM products, IM-products will also make HF-stuff audible. As perfectly demonstrated by the Sony.
Most amplifiers will show distortion below 0.1%. At 1khz. At 10 or 20khz ? :xeye:
Mike |
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| PMA |
| The amplifier model is SONY TA-FE320R. |
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| destroyer X |
They do all measurements.... and they know also all those norms, rules, regulations and what is annoying and what is not annoying.
They do measurements and also they invite factory people to many listening tests....their judgement, related quality, is made not only based in measurements....they also take into account the listening tests.
Reason why they have fame and money, beeing a giant Corporation.
All those guys had in University too....and many of them are audiophile too...also there are Marketing and costs to take into account when they decide something.
Hold on Boys...... a little bit slowly please....respect with those very good enginneers, yours coleagues, Professional friends of us.
regards,
Carlos |
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| mfc |
Hi,
Looks like the square wave in fig. 2.3 is 32Khz instead of 34Khz
(compare to the one right above it)?
Mike
p.s.
I've been doing some 4 tone simulations with one inband
signal at 6Khz and 3 out of band tones at 497.5Khz, 502.5Khz,
600Khz. This to simulate transmissions from am broadcast
band signals getting into the front end of an amp. Its
interesting how the number and amount of IM products from
the out of band signals can fall down into the audio band. |
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| PMA |
| quote: | Originally posted by mfc
Hi,
Looks like the square wave in fig. 2.3 is 32Khz instead of 34Khz
(compare to the one right above it)?
Mike
p.s.
I've been doing some 4 tone simulations with one inband
signal at 6Khz and 3 out of band tones at 497.5Khz, 502.5Khz,
600Khz. This to simulate transmissions from am broadcast
band signals getting into the front end of an amp. Its
interesting how the number and amount of IM products from
the out of band signals can fall down into the audio band. |
Hi Mike,
yes, the 34kHz is generated by function generator with quite low longterm frequency stability. But instant switch between sine and square shows well increase of intermodulation products.
Regarding 3 out of band tones, it is a very good idea.
Regards,
Pavel |
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| Werner |
Anyone of you familiar with the work of Paul Miller during the late 80s?
After an explanatory article 'Resonances and repercussions' he started testing amplifiers with as stimulus a sweep from DC to 100MHz plus (if I remember) a fixed tone in the audio band, and as output the noise spectrum in the audible band.
The results tended to correlate well with listening tests. |
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| gerhard |
| quote: | Originally posted by PMA
This is Symasym for 1kHz sine + 34kHz square: |
Why do we see these 1/f noise sidebands on the 34 KHz carrier in the symasym case but not on the Sony? (post 9 & 10)
How are the 2 generators combined? It could well be that they interact. For RF IMD measurements I do need filters, bridges and/or directional couplers to combine even two HP8662A generators or they intermodulate with each other before the device under test is even connected.
In the Sony case, some signals seem to be harmonics modulo 48 KHz.
Gerhard |
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| MikeB |
Possibly a fft-windowing artefact, the sony measuring has double the window size. Or, frequency of the 36khz is not stable enough, Or the soundcard... :scratch:
At least, it's not from the amplifier, as the directly measured signal shows the same symptom.
Gerhard, are these "Habanero Orange" in your avatar ? Chilihead ? :)
Mike |
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| gerhard |
| quote: | Originally posted by MikeB
Gerhard, are these "Habanero Orange" in your avatar ? Chilihead ? :)
Mike |
Yes, I grew a few this summer. Didn't get much orange habbies, but a lot of the chocolate hab. variety. They are _HOT_!
Gerhard |
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| PMA |
Gerhard,
have you reviewed the introductory document?
http://web.telecom.cz/macura/mixtest.html
There is a FFT measurement of generator (sum) signal itself. Do you see the same problem there?
The wider base of the 34kHz signal is caused by poor qaulity of that generator.
Sony was tested by my colleague, with different generator. |
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| PMA |
Guys,
anybody on Electronica in Munich Thursday next week? |
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| MaxS |
Hello all,
HF pollution are created by SMPS frequency and neon ligthing, radio emitter ( not the case of many people :D ). They are two types of transmission : by the wall plug. Too * fight * against it, i see two solutions : - Filtered IEC plug ( eg : Schaffner ... )
- Balanced power cord :D ( quite expensive, I assume )
In theory, the magnetic field of CD player PSU is very low and their metallic box make a electromagetnic shield who is polluting the Earth wire.
Is the HF interference came from Earth or by Neutral wire ? How can we clean them ?
( I hope to didn't hijack your topic Pavel )
Max. |
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| PMA |
Bon soir Max,
it is on-topic. I measured the interference at the output of multiformat player. It also spreads to another instruments through mains wires.
Salut,
Pavel |
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| gerhard |
> http://web.telecom.cz/macura/mixtest.html
>
> There is a FFT measurement of generator (sum) signal itself.
> Do you see the same problem there?
No, the summed generator signal looks OK.
> The wider base of the 34kHz signal is caused by poor qaulity of that generator.
> Sony was tested by my colleague, with different generator.
This explains the noise sidebands. Maybe it's a different sound card, too?
Talking about sound cards: Is there a clear winner to choose for measurements?
Are there any that start at DC?
Gerhard |
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| PMA |
| quote: | Originally posted by gerhard
> http://web.telecom.cz/macura/mixtest.html
No, the summed generator signal looks OK.
> The wider base of the 34kHz signal is caused by poor qaulity of that generator.
> Sony was tested by my colleague, with different generator.
This explains the noise sidebands. Maybe it's a different sound card, too?
Talking about sound cards: Is there a clear winner to choose for measurements?
Are there any that start at DC?
Gerhard |
Gerhard,
the problem is actually the function generator, it was measured separately. The sound card with the window used shows narrow spectral line in case that input is a good / stable generator.
Yes, my colleague used different sound card, but we had them well tested.
They do not start at DC. I can get to 1Hz order.
Regards,
Pavel |
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